<div class="d-flex align-items-center login-content" >
  <form [formGroup]="myForm" (ngSubmit)="onSubmit(myForm.value)">
    <h3 class="d-flex justify-content-center">用户登录</h3>
    <div class="form-group">
      <label for="userName" class="">用户名</label>
      <input type="text" class="form-control" id="userName" aria-describedby="输入用户名" name="userName" [formControl]="userName" [ngClass]="{'is-invalid':userName.invalid, 'is-valid':userName.valid}">
      <div class="valid-feedback">
        用户名格式正确!
      </div>
      <div class="invalid-feedback">
        <span *ngIf="userName.hasError('required')">
          用户名必须填写
        </span>
        <span>
          用户名长度必须大于3位,小于20位
        </span>
      </div>
    </div>
    <div class="form-group">
      <label for="password">密码</label>
    <input type="password" class="form-control" id="password" name="password" [formControl]="password" [ngClass]="{'is-invalid':password.invalid,'is-valid':password.valid}">
      <div class="valid-feedback">
        密码填写正确!
      </div>
      <div class="invalid-feedback">
        密码必须大于6位，小于16位
      </div>
    </div>
    <button type="submit" class="btn btn-primary btn-block" id="btnLogin">登录</button>
  </form>
</div>